This invention relates to an apparatus and method for applying a polymer coating to a desired length of an elongate member, preferably to an elongate intracorporeal device. More specifically, the invention relates to a method and apparatus for applying a polymer coating to a desired length of an intracorporeal guiding device or guidewire. The invention can also be used to apply a polymer coating to a length of any other suitable device such as a vascular stent, cardiac pacing leads, catheter tubings, braided or solid electrical wire, coaxial cable or the like.
In a typical prior art process for applying a polymer coating over an elongate member, an extrusion machine is used which has a heated die head with channels leading to a heated chamber within the die head. Melted polymer is forced into the chamber with a lead screw which forces solid polymer, usually in the form of pellets, into the heated chamber. The elongate member to be coated is passed through the back end of the die head into the chamber and out of an orifice in an extrusion die which is attached to the extrusion head. The elongate member is then pulled through the die as melted polymer is forced into the die head and onto the elongate member. Normally, the orifice in the die will be larger than the elongate member so that a desired amount of the melted polymer remains on the elongate member after passing through the orifice. After passing through the orifice, the melted polymer on the elongate device cools and the coating process is complete.
A prior art process such as that described above is well suited in many cases for coating long lengths of durable elongated members or substrate. The equipment used is large, expensive and cumbersome and can damage a fragile substrate being pulled through the device, such as a guidewire distal section with a small diameter helical coil. In addition, the amount of effort and expense required for a given set up often does not justify small runs of material. Also, the equipment is not well suited for coating short lengths of discrete elongated members, such as guidewires or the like, because adjusting the settings to achieve desired coating dimensions and parameters is usually a process that requires several minutes of running time in order for equilibrium of the dynamic to be established and stabilization of the process to occur. This often requires running many feet of substrate through the die head prior to stabilization which is not possible with a guidewire which is only several feet long.
Another difficulty exists in trying to vary the coating parameters dynamically in a controlled fashion in order to achieve a coating which has varying parameters such as a transverse dimension along an axial direction. As mentioned above, the usual coating equipment of the prior art is large and cumbersome and it is impractical to vary parameters such as temperature of the die, speed of pull, and pressure exerted on the melted polymer over short lengths of an elongate member substrate.
What has been needed is an apparatus suitable for applying a variety of polymer coatings to a discrete length of a fragile intracorporeal device substrate with quick response time for variation in extrusion parameters. What has also been needed is an apparatus suitable for coating an elongate intracorporeal member that has automatable control of extrusion parameters such as die temperature, pull speed and pressure applied to melted polymer which can produce repeatable control of diameter and other dimensions of the polymer coating applied. In addition, it is desirable to have an apparatus suitable for reliably applying a polymer coating with a constant outer transverse dimension to a substrate which varies in transverse dimension or diameter along its axial length.
The invention is directed to an apparatus for applying a polymer coating to an elongate intracorporeal device, specifically, a guidewire. In one embodiment, the apparatus can have a guide chamber with an input end having an input port and an output end. An extrusion orifice is disposed at the output end of the guide chamber and is in fluid communication with the guide chamber. The extrusion orifice can be configured to allow an elongate intracorporeal device or other substrate to pass through or be pulled through the extrusion orifice with a desired thickness or configuration of polymer coating on the elongate intracorporeal device or substrate. The orifice can be configured to leave a fixed thickness of polymer over the elongate intracorporeal device, or the orifice can be shaped so as to leave a desired profile or configuration of polymer coating on the device, e.g., an orifice having an oval, square or triangular cross section.
A heater member is disposed in thermal communication with the guide chamber and serves to heat a desired portion of the guide chamber. A cartridge advancement mechanism is disposed adjacent the guide chamber. In use, an extrudable polymer cartridge is placed within the guide chamber of the apparatus. The cartridge advancement mechanism can be configured to axially translate the extrudable polymer cartridge into the guide chamber in a direction of extrusion, i.e., a direction from the input end of the guide chamber to the output end of the guide chamber. The extrudable polymer cartridge can have a lumen extending longitudinally through the cartridge with the lumen being sized or configured to accept the elongate intracorporeal device. The lumen of the extrudable polymer cartridge is typically sized to allow the elongate intracorporeal member to slide freely within the lumen.
In another embodiment, a guide chamber is formed by a guide tube with the guide chamber being disposed within the guide tube. The guide tube has an input end with an input port in fluid communication with the guide chamber and an output end. A die having an extrusion orifice is disposed at the output end of the guide tube such that the extrusion orifice is in fluid communication with the guide chamber. The extrusion orifice of the die can be configured to allow an elongate intracorporeal device to pass through the die with a desired configuration of polymer coating on the member. A heater member is disposed in thermal communication with the guide tube for heating a desired portion of the guide tube or die.
A push tube is disposed at least partially and slidably within the guide chamber. The push tube has a contact end, an attachment end, a longitudinal axis and at least one inner lumen extending substantially parallel to the longitudinal axis of the push tube. The inner lumen of the push tube is configured to accept a desired elongate intracorporeal device. In use, an extrudable polymer cartridge, having similar properties to the extrudable polymer cartridge discussed above, can be disposed within the guide chamber between the extrusion orifice of the die and the contact end of the push tube.
In another embodiment, a puller is disposed adjacent the output end of the guide tube. The puller can be configured to be temporarily secured to a desired portion of the elongate intracorporeal device and apply a force and movement in the direction of extrusion on the device. A push tube actuator is disposed adjacent the input end of the guide tube and is configured to apply a force and movement on the extrudable polymer cartridge disposed within the guide chamber. Specifically, the push tube is disposed between the extrudable polymer cartridge and the push tube actuator and mechanically couples the push tube actuator to the extrudable polymer cartridge. A computing machine may be electronically connected to a temperature sensor coupled to the heater member, the puller and the push tube actuator. The computing machine can be used to repeatably control the temperature of the heating member, the rate of axial movement of the elongate intracorporeal device in a direction of extrusion by controlling the rate of axial movement of the puller, and the rate of feed or axial movement in the direction of extrusion of the extrudable polymer cartridge by controlling the rate of movement or force applied to the push tube in the direction of extrusion.
One of the advantages of the apparatus for applying a polymer coating is that many of the components of the apparatus can be manufactured from disposable polymer materials that are made to be modular and avoid the need for cleaning of components. For example, both the guide tube and the die can be made from a variety of high temperature polymers such as polyimide (PI), polytetraflouroethylene (PTFE), liquid crystal polymer (LCP) and polyetheretherkeytone (PEEK). This allows a subassembly consisting of the guide tube, die and extrudable polymer cartridge to be loaded into a corresponding guide tube assembly for each elongate intracorporeal device to be coated. When the device has been coated, the subassembly can be disposed of and a new subassembly loaded into the guide tube assembly. This eliminates the need for time consuming cleaning operations and allows the use of varying die configurations and extrudable polymer cartridge materials from one elongate intracorporeal device to the next.
Another advantage of the apparatus for applying a polymer coating is the ability to reliably maintain concentricity of the coating applied to the elongate intracorporeal device. Where such concentricity is desired, the use of an extrudable polymer cartridge having an inner lumen which is concentric to a longitudinal axis of the cartridge provides centering of the elongate intracorporeal device prior to passing through the extrusion orifice. As the extrudable polymer cartridge is melted at the output end of the guide chamber and applied to the elongate intracorporeal device, the unmelted portion of the cartridge immediately adjacent a melt zone of the extrudable polymer cartridge continuously provides centering of the elongate intracorporeal device within the guide chamber and extrusion orifice. Also, the melted portion of the extrudable polymer cartridge at the melt zone can be applied evenly in a radially inward direction from all sides of the elongate intracorporeal device in embodiments of the invention where the inner lumen of the extrudable polymer cartridge is concentric with the longitudinal axis of the cartridge. This can also facilitate maintaining concentricity of the polymer coating.
In use, an extrudable polymer cartridge is placed in the guide chamber of the guide tube between the extrusion orifice and the contact end of the push tube. An elongate intracorporeal device is loaded into the die, at least of a portion of the inner lumen of the extrudable polymer cartridge and optionally the inner lumen of the push tube. The elongate intracorporeal device is then temporarily secured to the puller and the heater member activated. When the portion of the extrudable polymer cartridge adjacent the die attains a desired temperature and viscosity, the puller and cartridge advancement mechanism, typically consisting of a push tube actuator, are activated. This advances both the elongate intracorporeal device and extrudable polymer cartridge in the direction of extrusion, i.e. in a direction from the input end of the guide chamber to the output end of the guide chamber.
The coating process can be terminated in several ways. The process may be terminated when an end or extremity of the elongate intracorporeal device is drawn through the output end of the guide chamber and die. This method will typically coat the entire end or extremity of the elongate intracorporeal device. Alternatively, the advancement of the extrudable polymer cartridge can be stopped by deactivating the cartridge advancement mechanism while continuing to advance the elongate intracorporeal device in the direction of extrusion. In this way, the melted extrudable polymer cartridge is no longer feeding into the extrusion orifice and coating the elongate intracorporeal device. Also, the amount of material in the extrudable polymer cartridge may be limited to suffice for coating only a desired portion of an elongate intracorporeal device. As the extrudable polymer cartridge is advanced in the direction of extrusion and polymer coating is applied, the cartridge gets shorter. The process continues until the contact end of the push tube hits the die and melted polymer material is no longer fed into the extrusion orifice and the coating process stops, although the elongate intracorporeal may continue to be pulled or advanced in the direction of extrusion.